1. Field of the Invention
The invention is directed to a low pressure drop filter for removing contaminants from gases, such as air, to a method of manufacturing the filter, and to a process of using the filter to remove contaminants from gases.
2. Discussion of Related Art and Objectives of the Invention
Indoor air pollution has become a serious and widely publicized issue of concern. Indoor air pollution has been linked to various health problems. For example, health problems have been associated with increased levels of formaldehyde emitted by the building materials, with carbon monoxide (CO) and sulfur gases, such as H.sub.2 S, SO.sub.2, and with mercaptans produced by natural gas combustion and cigarette smoke. In addition, air used for combustion in heating systems can contain chloride gases. With the currently-used high efficiency furnaces, outlet temperatures of such furnaces can be sufficiently low to cause condensation resulting in the formation of liquid phase hydrochloric acid (HCl) which is highly corrosive to metal furnaces and duct materials. It is, therefore, important to remove the chloride gases and mist containing such gases from the air.
Certain adsorbent materials have been used in the past for removing and/or oxidizing contaminants in air. For example, Gamson et al., U.S. Pat. No. 3,049,399, disclose the use of permanganates, such as permanganates of magnesium (Mg), sodium (Na), calcium (Ca), barium (Ba), potassium (K), and lithium (Li), to adsorb and oxidize odors from air. The permanganates are supported on a granular adsorbent, such as alumina. Such materials have also been supported on a variety of other supports, including alumina, silica, alumino-silicate, bauxite, and clay.
Muhlratzer et al., U.S. Pat. No. 4,761,323, disclose a filter, particularly a soot filter, comprising a fiber bat manufactured by impregnating or wetting the fibers with a colloidal sol, the excess of which is drawn off and the fiber material dried and sintered at a high temperature (e.g., about 900.degree. C.). The sintered fiber bats may be subsequently treated, e.g., by coating the bats with a catalytically active material. The resulting ceramic structure is preferably used as a filter for an exhaust gas from internal combustion engines.
Brooker et al., U.S. Pat. No. 4,797,318, disclose a non-dusting, non-woven material comprising a web of meltdown fibers of an organic adhesive polymer containing adsorbent particles of activated carbon, potassium permanganate, baking soda, clays, diatomaceous earth, and activated alumina, as well as potassium permanganate complexes. The adsorbent particles are incorporated into the stream of meltdown fibers while the fibers are still tacky. The material can be used for gas/vapor filtering and/or adsorbing, specifically for disposable vacuum cleaner bags.
Pearson et al, U.S. No. 4,639,259, disclose the use of alkaline earth compounds supported on activated alumina for removing chlorides from industrial gas streams, such as reformer gas (containing principally hydrogen), and other refinery gas streams.
Kanno, U.S. Pat. No. 4,003,979, discloses a method of cleaning air containing carbon monoxide (CO) comprising removing from the air materials capable of reducing at ambient temperature the oxidization activity of a noble metal catalyst, and, subsequently, passing the air at ambient temperature through a catalyst layer composed of the noble metal catalyst supported by active carbon. The catalyst layer contains 20 to 50% by weight of water, based on the total weight of the noble metal catalyst and the active carbon. The active carbon particles containing the noble metal catalyst can be adhered onto a honeycomb-like structure by applying a conventional adhesive on the honeycomb-like structure and then depositing the active carbon particles thereon.
McAllister, U.S. Pat. No. 4,155,358, discloses a disposable valveless chemical cartridge respirator for filtration of a vinyl chloride monomer from air comprising an activated alumina coated with a color enhancing coat of manganese dioxide and with potassium permanganate. The potassium permanganate is used to indicate the end of the useful life of the cartridge.
Gens, U.S. Pat. No. 4,550,098, discloses methods for purification of mixed gas streams, containing hydrogen sulfide, carbon dioxide, carbon monoxide, sulfur, hydrogen, methane, and other hydrocarbon gases, with an oxidizing reactive solid. The oxidizing reactive solid has a general formula D-M-O, wherein D is chosen from the alkali metals or alkaline earth metals, such as sodium, potassium, lithium, calcium or magnesium; M represents a transition metal selected from the group comprising manganese, copper and iron, and Groups IB, VB, VIB, VIIB or VIII from the Periodic Table of Elements; and O designates oxygen. Optionally, the reactive solid may contain alumina, e.g., Example II.
Wisnewski et al., U.S. Pat. No. 3,822,531, disclose an automobile exhaust gas filter made, for example, of fiberglass, stainless steel wire, or asbestos. When the filter is made of fiberglass, a binder is preferably affixed to the fiberglass to ensure its thermal stability at high temperatures. Preferred binders are colloidal silicas, such as "Positive Sol 130 M and Ludox HS-40."
Activated alumina has wide use in hydrogen fluoride (HF) alkylation operations, where HF and organic fluorides carried over from the alkylation operation are scavenged from the gas stream by the alumina. In use, granular, or differently shaped forms of, alumina (i.e., spheres or extrudites) is packed into a bed and the gas to be cleaned is exposed to the bed of material.
It has also been proposed to use particles of alumina comprising a salt of permanganic acid to remove contaminants from other gases. In one example of this technology, air is forced through a filter comprising a packed bed of granular or spherical material for oxidizing the impurities from a building air. Such a packed bed of material can add a very significant airflow resistance potentially overloading or reducing the efficiency of the blower system used to circulate the air. If an existing air handling system is used, much of the air must be bypassed around the filter to alleviate the pressure drop attributed to the filter. This results in an incomplete exposure of the air to the adsorbent or oxidant. If complete exposure is desired, larger blowers are often required to overcome pressure drop. Although such a solution may be practical in certain industrial or commercial applications, it is prohibitively expensive in the residential and light commercial market segment.
Low pressure drop fiber filters have been widely used in residential and commercial heating/air conditioning applications as a means of removing airborne dust particles. However, no suitable method has been developed to make the aforementioned adsorbents, such as silica or alumina, in fibrous forms for filters to achieve low airflow resistance.
Accordingly, it is a primary objective of this invention to provide a low pressure drop filter comprising an adsorbent coating, such as silica or alumina, for removing contaminants from a gas, such as air.